Rotatable tremulant sound producer



Nov. 29, 1949 D. J. LESLIE ROTATABLE TREMULANT SOUND PRODUCER '7Sheets-Sheet 2 Filed July 9, 1945 NVENTOK w. 6 //N R $0 f JA M m 0 Nov.29, 1949 D J. LESLIE 2,489,653

' ROTATABLE TREMULANT SOUND PRODUCER Filed July 9, 1945 7 Sheets-Sheet 4Tic. 15

I NV ENTOR 5000/0 j Kai/f6 BY m WATTORNEY Nov. 29, 1949 n. J. LESLIE2,489,653

RQTATABLE TREMULANT SOUND PRODUCER Filed July 9, 1945 7 Shets-Sheet 5ATTORNEY Nov. 29, 1949 D. J. LESLIE ROTATABLE TREMULANT SOUND PRODUCER'7 Sheets-Sheet 6 Filed July 9, 1945 0; TONE \NVENTO'R 0000/0 'Nov. 29,1949 D. J. LESLIE 2,489,653

ROTATABLE TREMULANT SOUND PRODUCER Filed July 9, 1945 '7 Sheets-Sheet 7\NVENTOR Dana/d J [as/A's BY l/ ATTCfz'.

Patented Nov. 29, 1949 UNITED STATES FATENT OFFICE ROTATABLE -'1REMULANTSOUND PRODUCER.

JAN 9 1951 Donald J. Leslie, Wilmar, Calif.

Application J,u1 y 9, 1945, Serial No. 603,850

"10, 1940, in the name of Donald J. Leslie under Serial No. and entitleddevice.

In playing an ordinary musical instrument,

as a stringed or wind instrument, or in singing,

369,4 13, Acoustic This vibrato efiect, in the rapid motion of thefinger on the appropriate key or string, and which causes cyclic andrapid minor variations of pitch.

It is an object of this invention to impose pitch tremolo or vibrato, bymechanical means, on a musical tone.

It is another object of this invention to provide means for operatingsound producers incorporating air actuators to secure vibrato effects ina simple and effective manner.

It has been found that cyclic motion at an appropriate rate of a channelforming means utilized for transmitting a tone suffices to impartvibrato to the tone. Thus, it is another object of this invention toobtain vibrato or tremolo effects by cyclic motion, such as may be pro.-duced by rotation of a sound transmitting channel.

It is another object of this invention to pro.- vide a horn or othermeans forming a sound channel having special radiating properties,whereby the character of the vibrato is improved.

It is another object of this invention to pro.- vide an arrangementwhereby it is possible to alter the character of the vibrato.

It is known to provide apparatus which, by appropriate synthesis ofelectrical currents, pro.- duces tones which have timbres the same astones produced by any ordinary musical instrument. An electric organ,for example, is capable of producing tones having the characteristicsound of organ tones, although no organ pipes are utilized. It isanother object of this invention to produce a pitch tremolo bymechanical means in ,such electrical apparatus.

When sound comes from a restricted locality, there are directional andother effects that are undesirable. It is still another object of thisinvention to avoid this point source efiect.

' This invention possesses many other advanmore clearly apparent from aconsideration of several embodiments of the invention. For this purposethere are shown a few forms in the drawings'accompanying and formingpart of the present specification. These forms Will now .be described indetail, illustrating the general principles of the invention; but it isto be understood that this detailed description is not to be taken in alimiting sense, since the scope of the invention is best defined by theappended claims.

In the drawings:

Figure 1 is .a pictorial view of a cabinet used for housing one form ofthe apparatus;

Fig. 2 is .a rear elevation of the cabinet, a part of the cabinet beingbroken away;

Fig. 3 is a section on an enlarged scale, as seen on plane ,3-3 of Fig.2;

Fig. i is a detail section as seen on plane 4- .4 o Fi 2;

Figs. 5 and 6 are fragmentary detail sections, as seen oncorrespondingly numbered planes of Fig. 2;

Fig. 7 is a detail section .on an enlarged scale, as seen on plane 'l'|of Fig. 5

Fig. 8 is a detail section on an enlarged scale, ,asseen on plane 8--8of Fig. 6;

Fig. 9 is a section similar to Fig. 4, but of a modified form of theinvention;

Fig. 10 is a transverse section, as seen on plane Figs. 11 to 14inclusive are diagrammatic showings of modified forms of the apparatus;

Fig. 15 is a view similar to Fig. 2, showing a modified form ofapparatus;

Fig. 16 is a vertical section, showing another 'modified form ofapparatus;

Fig. 17 is a plan view of the apparatus of 40 hand side of Fig. 16;

Fig. 19 is a view similar to Fig. 18, but show.- ing still anothermodified form of apparatus;

Fig. 20 is a diagrammatic showing of another modified form of apparatus;

Fig. 21 is an elevation of a further modified form of apparatus;

Fig. 22 is an elevation as seen from the left.-

hand side of Fig. 21;

Fig. 23 is a diagrammatic showing of another modification of theinvention;

Fig. 24 isa schematic showi g of still another form of apparatus;

Fig. 25 is a fragmentary section on an enlarged scale, taken asindicated by line 2525 on Figf24;

Riisiiiiit tages, and has other objects which may be made Fig. 26 is aview similar to Fig. 25, showing a further modification;

Figs. 27, 28, and 29 are diagrams of radiation patterns useful inexplaining certain aspects of the invention; and

Fig. 30 is a fragmentary view similar to Fig. 24, showing a stillfurther modification of the invention.

When a tone is to be produced by electrical means employing apparatusincluding a loud speaker, the invention makes it possible to provide atremolo effect in a simple manner; more specifically, by providing asound transmitting channel for association with the apparatus, andcausing the mouth of this channel to rotate. For example, in one form ofthe invention, this mouth may serve to emit the sound from the speaker,the rotation thereof being such as to cause the mouth to movealternately toward and away from the hearer at a frequency correspondingto the vibrato. In another form of the invention, the sound transmittingchannel may serve to transmit sounds from an appropriate source of toneto a microphone which, in turn, passes current impulses to the speaker.In this case, the rotation of the sound channel is such as to cause themouth, which receives the tone from the source, to move toward and awayfrom the source. In either case, the pitch of the sound heard by thelistener is alternately increased and decreased.

It has been determined experimentally that the vibrato not only impartsa pleasing gliding quality to the tone, but also determines the richnessof the tone. For such a result, the speed of rotation should be betweenabout 300 and 450 revolutions per minute, producing a tremolo of betweenfive and seven cycles per second. At rates below these, the tone doesnot give singleness of pitch, the disturbances in the pitch beingperceived as occurring successively in the tones. Furthermore, therichness of the tone is reduced. At rates above these, the richnessgives way to an experience of increased complexity, and the glidingcharacter of the tone is lost. Accordingly, the rate of rotation of thesound channel is confined between narrow limits.

In order to produce the proper vibrato effect, the speaker through whichthe sound passes may be moved cyclically between five and seven cyclesper second, as by rotating the speaker.

A rotatable speaker has certain drawbacks, such as the need of rotatinga relatively heavy object and of providing a slip ring connection topass modulated current to the speaker. The same results may be obtainedby providing a stationary speaker, or other sound generator, with adirectional horn which is rotated about the speaker. Such an arrangementis shown, for example, in Fig. 2 of the drawings. On the other hand, arotatable speaker is easily connected with the directional horn; andthere is no attenuation of high frequencies due to the need of employinga horn providing a bend, as in the case of a stationary speaker. Such arotatable speaker is shown in Fig. 21.

Similar results are also obtainable by providing a revolving microphonewhich feeds into a conventional speaker. Since a microphone so arrangedmoves alternately toward and away from the source of the sound which isbeing picked up, the pitch of the sound picked up and transmitted to thespeaker, or other transducer such as a recording mechanism, will vary.An arrangement of this kind is shown diagrammatically in Fig. 23.However, to avoid the inherent difilculties of a rapidly movingmicrophone, such as vibration and the need of slip ring connections forthe microphone current, it may be preferable to use a revolvingdirectional horn which feeds the sound to a stationary microphone. Suchan arrangement is shown diagrammatically in Fig. 11.

Referring to Fig, 2 of the drawings, a high frequency speaker or soundgenerator I and a lower frequency speaker or sound generator 2 are shownas housed within a cabinet 3. Associated with each speaker respectivelyare means forming directional horns 4 and 5 (see Figs. 5 and 6). Each ofthese horns forms a sound channel having a mouth or sound emittingopening spaced from the axis of rotation. The horns 4 and 5 arerotatably supported in the cabinet 3 and are arranged to be rotated bymotors l and 6 respectively. To allow the sound from the speakers topass out of the cabinet freely, a number of openings are provided. Thus,near the bottom, each side, as well as the front and back of the cabinethas openings, such as 8, 9, and ID (Figs. 3 and 6) which may be coveredby louvres or grills [2, or by a loose fabric as shown at i3. Theseopenings are for the lower speaker 2. The entire top of cabinet 3 isopen except for a covering M of light fabric which permits free passageof sound from the upper speaker I.

As the horns 4 and 5 are rotated, the pitch of the sound reaching thelisteners ear from the speakers varies and, as previously discussed, byappropriately choosing the speed of rotation, a pleasing vibrato effectis obtained, as well as maximal richness of tone.

Also, since the sound is not received by the ear from a fixed andlimited area, but, instead, partly from an area whose position iscontinually changing and partly by reflection from surrounding walls andadjacent objects, a pleasing sense of space and depth of tone isobtained, and the phenomenon of a point source is avoided.

Referring in more detail to the apparatus, the cabinet 3 is permanentlyclosed on the front and sides 28, 2|, and 22, and is partly closed onthe back by a removable panel 24. Cabinet 3 is also provided with anupper shelf 25 (Figs. 2, 5, and 7) for supporting the high frequencyspeaker I, together with its horn 4 and driving motor I, and a lowershelf 25 (Figs. 2, 6, and 8) for supporting the low frequency speaker 2.

As before mentioned, the apparatus is intended for use in connectionwith an electronic device. Thus, the final amplifier stages of such adevice may be conveniently placed on the upper shelf 25, as indicated by2'! (Fig. 2), and connected by means of a suitable cable '28 with thedevice, such as an electric organ. The amplifier 27 may be connectedwith the speakers i and 2 by suitable cables (not shown) in aconventional manner, a suitable dividin network generally indicated by29 (Fig. 2) being interposed in the connections to limit the frequenciessupplied to the respective speakers. The connections between anappropriate amplifier and high and low frequency speakers are wellunderstood by those skilled in the art and, accordingly, will not be detailed here. Appropriate leads (not shown) also supply current to motors6 and I, switches I5 and 16 (Fig. 2), located on the exterior and nearthe top of cabinet 3, servin to control the motors respectively.

As clearly shown in Figs. 5 and 7, the high frequency speaker I issecured to the underside of *a rectangular plate 30, as by screws 3|.Plate may be of suitable relatively light material which machinesreadily, such as fibre, and is supported with respect to shelf 25 by abox-like frame 32. Plate 33 is provided with a central bore 33 which isaligned with the speaker opening 34. Bore 33 is provided with acounterbore 35 which has an anti-friction radial and thrust bearing 36mounted therein. A long set screw 31, threaded into the fibre plate 36,engages the outer race 38 of bearing 36 and secures bearing 36 in plate36. A pulley 39 with a flat upper face 46 has a tubular hub 4| which issecured to the inner race 42 of bearing 36, as by a headless set screw43.

Mounted on the upper face 4|] of pulley 39 is a horn 4, which hornextends upwardly and away from the opening 41 in hub 4|. Horn 4 ispreferably an exponential type horn, and serves to direct the soundwaves from speaker I, these waves passing out of cabinet 3 through theopen top thereof. To maintain the horn 4 in mechanical balance, asimilar horn 48 may be mounted diametrically opposite horn 4. The soundwaves, however, do not enter horn 48, a wall 49 serving to separate horn48 from horn 4.

It is important that vibrations from the rotating apparatus be preventedfrom reaching the cabinet. Accordingly, plate 36 is resiliently supported on frame 32; and frame 32 is, in turn,

resiliently supported on shelf 25 by means of rubber bushings 50. Thesebushings 50 each have a cylindrical body portion 5| surmounted by aflange 52, and are mounted inpairs by being inserted in a suitably sizedopening 53 in the member to be supported, the flanges 52 engaging theopposite faces of the member. A screw, as 54, is then passed through acentral opening in the bushings 5|] into the supporting member, as 25, asuitable washer 55 being interposed between the head of screw 54 and theflange 52 of the top bushing 50. In this manner, the lower flange 52 isinterposed between the member 30 or 32 and its support, the bushingsalso preventing the screw 54 from directly contacting the supportedmember. Thus, transfer of vibrations between the-horn and its support iseffectually prevented.

The motor rotates the horn 4 by means ofa belt 51 engaging pulley 39.The motor I may be adjustably supported on a bracket 58 in cabinet 3,suitable means such as resilient pads 59 being provided between thebracket and the cabinet to prevent vibration from the motor I reachingthe cabinet.

The low frequency speaker 2 is also provide with a revolving directionalhorn 5 (Figs. 2, 3, 4, and 6) which, however, is shown as not being ofthe exponential type. Horn 5 is built of upper and lower discs 6| and62, joined by vertical walls 63. The top disc 6| is provided withopenings 64 to admit the sound from the speaker 2, the sound passingoutwardly through opening 65 in wall 63. The lower disc 62 isimperforate.

The horn 5 is mounted on a central, vertical shaft 66 which is rotatablysupported by antifriction bearings 6'! and 68 at its upper and lowerends respectively. Bearings 61 and 68 are respectively supported infibre blocks 69 and Ill.- Block 69 is supported on a bar 1| spanning anopening 12 (Fig. 8) in the shelf 26, which opening serves to pass thesound waves from speaker 2 into horn 5. To prevent undesirable transferof vibrations between horn 5 and the cabinet 3, the block 69 issupported on bar H by means of rubber bushings 15 and screws 16 in amanner outside surface of the cone 85.

6 analogous to that in which bushings 56 support plate 30 and frame 32on Fig. 5. Block 1|) for the lower bearing 68 is similarly supported ona bar 11 (Fig. 9) extending diagonally across the bottom of cabinet 3.

A pulley i9 is mounted on the outside of disc 62, a belt passing overthe pulley and operatively connecting the horn 5 with motor 6 (Fig.

3). The motor 6 is adjustably mounted in cabinet 6 by brackets 8|,resilient pads 82 being interposed between brackets 8| and the wall 2|which supports them to prevent any vibration from the motor 6 reachingthe wall or the cabinet. It is to be understood that the horn structure6|, 62, 63, etc. is rotatively balanced with respect to shaft 66. Toreduce the resistance imposed on its rotation by the surrounding air,the peripheries of discs 6| and 62 may be joined by a piece of lightfabric |3|. This, in effect, makes the structure cylindrical andeliminates fanning of the air as the structure is rotated.

To improve the quality of the low frequency production, it may bedesirable to use the refiex principle. The low frequency speaker 2 isshown as of the type having an air actuating cone 85 of large diameter,for example, fifteen inches. Speaker 2 is supported above horn 5 withcone 85 directed downwardly and axially aligned with the horn by meansof a table 36 (Fig. 6). Table 86 comprises a board or plate 3?, whichmay be square for convenience of fabrication, spaced above shelf 26 ashort distance by means of blocks 88 at the corners of plate 8i. Plate8? supports the speaker 2 by having frame 83 of the speaker secured tothe plate. This plate 8? is provided with a central aperture of adiameter somewhat less than that of cone 35, and a tube 9| extends fromaperture 66 down through opening 12 in shelf 25 to disc 6|, terminatingabove the disc 6| to provide suitable running clearance. Thus, soundwaves from the lower, or inside, surface of cone 85 pass into horn 5without mingling with the sound waves from the upper or These lattersound waves pass downwardly in the space between plate S'l and the sidesof cabinet 3, and enter horn 5 through the annular space 32 definedabout tube 9| by the opening '52.

While the speakers have been shown and described as mounted in a singlecabinet, this is merely a convenient way of assembling the apparatus,and makes a compact and readily portable unit. The speakers could be inindiv'dual cabinets and spaced apart if desired. Further, additionalspeakers may be provided for either frequency if desired.

7 Further, it is not necessary that the horns from the high and lowfrequency speakers rotate in synchronism; in fact, best results arefrequently obtained by rotating the speakers at different speeds and inopposite directions.

As an alternative to providing the fabric |3| directly on the structure5 to reduce the wind resistance, a well I68 may be formed in which thestructure 5 revolves, as shown in Figs. 9 and 10. This similarlyprevents fanning of the air by the rotating structure. The horn 5 ssupported between bar H on shelf 26 and diagonal bar 11, all as before.A ring I 6 formed of a light metal angle and having a diameter slightlygreater than that of the horn structure, is mounted on the under side ofshelf 23. A similar ring m2 is mounted on the upper side of bar 71.Fabric I03 7 encircling the horn structurev is secured between theangles.

The effect secured by the rotation of the horns, as heretofore stated,ismost satisfactory when the speed of rotation is about 400 revolutionsper minute, and which fixes the cyclicvariation of pitch at the rate ofabout seven cycles per second. The actual variation in pitch is afunction of the instantaneous relative linear velocity of the sourcewith respect to the ear; and this depends, in part, upon the radius ofthe eccentricity of the mouth or sound emitting opening of the horn tothe axis of rotation. This distance is represented, for example, by theradius of the drum 45 of Fig. 5, and may chosen to suit the particularapplications; for example, the radius may be as little as three inchesor as much as a foot or two.

That the rate of seven cycles per second is an optimum is shown in thework Hearing by Stevens and Davis, published by John Wiley and Sons, atpages 234 to 241. Apparently, this seven cycle value must be closelyapproached to obtain the most pleasing effects.

As previously mentioned, a tremulant efiect is similarly obtainable byproviding a stationary microphone with a rotating directional soundchannel forming means feeding sound to it. Thus, in Fig. 11, amicrophone of any preferred type is indicated by I Ill and is shown asprovided with a directional horn III, rotatably supported by ananti-friction bearing H2. A motor H3 rotates horn I I i at the desiredspeed by means of a belt H4. The sound emanates from a source H5, asuitable sound-proof enclosure II 8, indicated by broken lines, beingprovided to enclose the source and the microphone.

The impulses from the microphone are amplified by a suitable amplifierH6 and are then fed to a speaker I I1, which may be a conventionalspeaker or speakers, or may be a conventional recording apparatus.

It is also possible to combine the rotating speaker arrangement with therotating microphone. Such an arrangement is indicated in Fig. 12,wherein a speaker I20, having a directional horn I2I rotated as by amotor I22, is substituted for the translating device I I1 of Fig. 11.

It is sometimes desirable to vary the apparent strength of thetremulant. This may be done conveniently by arranging that only aportion of the entire sound produced will have tremolo, and by providingmeans whereby the amount of this portion relative to the total sound maybe altered at will. There are several ways in which this can be done.Thus, in Fig. 13, a rotating directional horn I25, driven by a motorI26, is used to dis tribute the sound from a stationary speaker I21. Asecond speaker I 28 is provided with a stationary horn I29; and speakersI21 and I28 are connected to a common amplifier I30 by a dividingnetwork I3I including a potentiometer I32.

By adjusting the position of arm I33 of the potentiometer I32, theresistance value in circuit with each speaker may be altered, withresultant changes in the amount of sound delivered by each speaker. Itis to be understood that either the high frequency speaker and horn, orthe low frequency speaker and horn of Figs. 2 and 3 may be replaced by acombination such as disclosed in 13, or that the high and low frequencyspeakers may each be replaced by such an arrangement, adapted toreproduce high and low frequencies respectively. It is also to beunderstood that speaker I28 may equally Well be of some type notrequiring a horn.

In Fig. 15, a cabinet 3 is shown which houses a high frequency speaker Iand a low frequency speaker 2, provided respectively with rotatingdirectional horns 4 and 5. These speakers are fed from a commonamplifier 21 through appropriate cables indicated diagrammatically, adividing network 23 being interposed to limit the frequencies suppliedto each speaker, all as shown in Fig. 2. In addition to the highfrequency speaker I, another high frequency speaker is shown at I15.This speaker I15 may have a stationary horn i1 ii to emit sound upwardlyfrom the cabinet, and is arranged to be fed from a dividing network E11,similar to that shown at I3I of Fig. 13, and interposed in the leads tospeaker I.

A second low frequency speaker may also be provided and is indicated atI13. This may be of the moving cone type wherein no horn is utilized,the sound being emitted through a suitable opening I18 in the side ofcabinet 3. This speaker I18 is fed from an appropriate dividing circuitI33 interposed in the leads to speaker 2.

It is possible to use a single speaker and to divide the sound therefromso that some of it has a tremuiant effect while the remainder does not.ihus, in Fig. 14, a stationary speaker I36 delivers sound to a rotatingdirectional horn I31. Suitable means are provided for varying thedistance of the mouth I38 of horn I31 from the speaker I36, thusproviding a variable opening permitting some of the sound waves to passfrom the speaker without passing through the revolving horn I31.

One way in which such a variable opening can be provided will now bedescribed. Horn I31 is rotatably supported by means of a radial andthrust bearing I39 on a movable platform I40, which also carries motorMI for driving the horn. Platform I40 is guided for vertical movementwith respect to the speaker I36 by suitable guide bars I43 on a baseplate I42, and is adjustably supported with respect to the base plateI42 by a threaded rod I44 engaging nut Hi3 fixed on platform I 30. RodI44 is rotatablysupported in fixed axial position with respect to baseM2 by a suitable bearing I43 and is arranged to be rotated by a handcrank I41 through intervening gearing I43. Obviously, if horn I31 ispositioned immediately adjacent horn I35, practically all sound from thespeaker will have tremolo. By moving the horn I31 downwardly so that itsmouth I38 is spaced from the speaker, some of the sound from the speakerwill pass directly to the hearer without passing through the horn; hencewill have no tremolo. The rest of the sound will pass through the hornand have tremolo. By varying the spacing between the mouth I38 of hornl31 and speaker I36, the strength of the tremolo can be varied.

In several forms of the invention so far described, the vibrato isobtained by cyclically moving an opening through which the sounds areemitted toward and away from the listener, as by rotating a directingsound horn which provides such opening. With a rotating horn, the rateof movement of the mouth toward and away from the listener is a functionof the angular position of the horn, as well as of the length of thehorn, such rate of movement approaching zero as the horn approaches aposition pointing directly at the listener. Thus, the frequency changeand the vibrato also approach zero. Further, the amplitude of the soundis at a maximum with respect to the listener with the horn pointing athim, which further reduces the vibrato efiect.

By modifying the usual radiation pattern of a sound horn to obtainbroader distribution of listener at any given moment. For this purpose,-the horn mouth, or other sound emitting opening, should be narrow or ofsmall angular extent in the plane of its rotation.

A speaker adapted for operation in the lower frequencies requires amouth opening of considerable area; the mouth shape is thus preferablysuch that its dimension parallel with the axis of rotation issubstantially greater than its dimen-'- sion in the plane of itsrotation. A horn of this nature is illustrated in Figs. 16, 1'7, and 18.

It can be shown that such a horn, having an opening with a dimension inone direction equal to several wave lengths of the sound emitted, andwith a dimension in the other direction of less than one-quarter of sucha wave length, is highly directive in the plane of its length, or longdimension, but has a broad radiation pattern in the plane of its width,or short dimension. Thus,

a horn with a mouth of this character has the double advantage ofproviding a broad radiation pattern, as well as causing all of theemittedsound to advance with respect to the listener at a more nearlyconstant instantaneous speed.

In Figs. 16, 1'7, and 18, a speaker I8I is shown which may be of thetype employing a moving cone as the air actuator. The speaker issupported within a casing I82, and with its axis vertically disposed, bybeing secured to the top wall I83 of the casing I82. The casing orenclosure serves to prevent radiation from the back of the speaker cone,and may be filled with rock wool or other sound absorbent material. Anopening l83-a in the top wall I83 serves to transmit sound waves fromthe speaker i8I to a horn I84 mounted on the casing I82 for rotationabout the speaker axis I35. As clearly shown in Figs. 17 and 18, themouth IBd-a of the horn I84 is quite narrow in the plane of rotation ofthe horn to ensure that sound waves emitted by the mouth all move atsubstantially the same speed with respect to a listener, as well asproduce a broad radiation pattern. At the same time, the mouth I84-a isquite long in a direction parallel with the axis to provide thenecessary area.

The horn I84 is supported and guided for rotary movement by means of astationary vertical shaft I85 mounted in a bar I81 extending across theopening I93a and fixed to the top casing wall I83. This shaft I86extends through the upper wall of the horn I84 into a thrust hearingstructure I88, a hardened ball I529 therein supporting the weight of thehorn by engagement with the end of the shaft I85. A radial bearing I90,supported in the throat of the horn by a bar I9I extending across thethroat of the horn and engaging the rod I86, serves to guide the bornfor rotary movement about the rod I9 5.

A counterweight I92 adjustably mounted in an arm I 93, extendingradially from the thrust bear ing I88 opposite the horn I84, serves tobalancethe weight of the horn I84 about the supporting ball I39, thusreducing the pressure on the radial bearing due'to the weight of thehorn, as well as maintaining the horn in rotating balance.

The horn I84 is arranged to be rotated at an appropriate speed, aspreviously discussed, by a small electric motor I94 mounted on thecasing I82, and connected by a belt I95 to a pulley structure I95secured about the throat of the horn."

A ring Isl is provided about the opening I93a.

and telescopes into the throat I84-b of the horn I84 for sealing againstescape of sound passing from the speaker ISI to the horn.

The character of the vibrato may be varied by;

providing rotating horns, such as just described,

with differently proportioned mouths; for ex ample, with mouthsvariously inclined in the direction of rotation. Fig. 19 is a front viewsimi-i lar to Fig. 18, and shows a horn 2% which has a mouth 2flta, thelong dimension of which is oblique with respect to a plane normal to theaxis of rotation. This angle of obliquity may be chosen as desired, asindicated by the mouth outlines 200-?) and 200-0.

A rotating horn, such as any of the types so.

far discussed, may be employed as shown schematically in Fig. 20 toimpart vibrato to a steady tone as from a source 20L fixed microphone202 to supply modulated current to an amplifier 203 operating a speaker204. The sound from the speaker 204 is fed to a directional horn 205,supported for rotation about a vertical axis by a bearing 206 andappropriately Therein, a speaker 2I0 of any suitable type is,

shown as enclosed in a casing 2I I which may be filled with soundabsorbent material to prevent sound radiation from the back of thespeaker.

of the casing 2H and of considerable length parallel with the axis ofrotation, thus providing the advantages of a narrow source and a broadradiation pattern, as.

previously discussed.

The speaker ZIII and the horn 2I2 are supported for rotation about avertical axis 2! as by the casing 2 being secured to a vertical shaft2I5 rotatably supported by a suitable bearcurrent is fed to the speaker2H1 by means of The horn 2I2, being. without bends, does not materiallyattenuate;

slip rings 220 and 22I.

the higher frequencies.

In the form shown in Fig. 23, a rotating microphone 223 is provided forreceiving tone This tone affects a.

from a source 224. The microphone 223 is supported for rotation about avertical axis by a bearing structure 225, and is arranged to be drivenat an appropriate speed by means of a motor 226. Current from themicrophone 223 is fed by means of a slip ring connection 221 to anamplifier 228 which actuates a speaker 229. It is not necessary thatthis speaker have a rotating channel or sound emitting opening, sincethe desired vibrato is imposed by the rotation of the microphone 223.

For frequencies where a large opening is required, the horn justdescribed may be preferred. However, horns of rather small dimensionsare commonly employed for medium and high frequencies. Such a horn canbe readily fitted with some type of deflector at its mouth for alteringthe radiation pattern of the horn and obtaining smooth vibrato. Anarrangement of this sort is shown in Figs. 24 and 25. In Fig. 24 adirectional sound horn 235, adapted to transmit sound from a source 236,is arranged to be rotated at a. suitable speed about axis 231, spacedfrom the mouth of the horn, as by a motor 238.

Such a horn will have a radiation pattern of the form indicated by thebroken lines in Fig. 27. The sound emitted will have a peak amplitudedirectly in front of the horn, the higher frequencies having stronglydirectional characteristics as indicated by the curve marked A, and themedium frequencies being more widely distributed as indicated by thecurve B.

By providing a deflector comprising a pair of plates 239 and 240.oppositely inclined across the mouth of the horn 235 in the plane ofrotation of the horn, the radiation pattern may be changed to have aform such as that indicated by the wave C in Fig. 28. Therein, it willbe noted that the peak amplitude in front of the horn has beensubstantially reduced and the sound distributed over a Wider area.Furthermore, the directional properties of the higher frequencies havebeen decreased so that these and the medium frequencies have about't'hesame distribution. Such a deflector also affects the vibrato byincreasing the apparent length of the horn which increases the Dopplereffect. e

As shown, theplates 239 and 240 are large with respect to the mouth ofthe horn 235, and are disposed at right angles with respect to eachother.

Different radiation patterns may be provided by utilizing larger orsmaller plates for a difierent inclination, or both. Thus, in Fig. 26,several pairs of smaller plates 2-H and 242 more steeply inclined areshown as provided across the mouth of the horn 235. The radiationpattern for ahorn with such 'a deflector will 'be of the type indicatedin Fig. 29, and is generally intermediate the curves A and B of Fig. 27and the curve C of Fig. 28. The amplitude peak directly in front of thehorn is not very pronounced and the sound is quite broadl distributed,the medium frequencies (curve D) being somewhat more widely distributedthan the higher frequencies (curve E).

The directional characteristics of a horn in the plane of rotationstrongly aifect the vibrato, while the same characteristics in a planenormal thereto have no effect. Accordingly, if a horn with differentdirectional effects in the two planes is arranged so that itsdirectivity is effective in either itspla n'e of "rotation or at 90thereto, compi'etely different effects can be obtained. Other efl'ec'tscan also be obtained by positioning the horn directed in an intermediateposition.

To permit such adjustment of the mouth, the

horn 235 is formed of two sections 235--a and 235-1), rotatably coupledby a collar 225c. Thus, the outer end section 235a, which has differentdirectional properties in different planes by virtue of the deflectorplates 39 and 349, or 241 and 242, may be adjusted to vary the vibrato.A set screw 243 serves to secure the horn section 235-a in adjustedposition.

It may be desirable to provide a deflector which will produce the sameradiation pattern in ail planes. For this purpose, a horn such as 235may have a conical deflector 245 suitably supported at its mouth, asshown in Fig. 30. Qbviously. the proportions of the cone may be variedto produce different characters of vibrato.

The aspects of the invention illustrated in Figs. 16 to 19, inclusive,21, 22 and 24 to 39, inclusive, form the subjects matter of divisionalapplications Serial No. 90,649, filed April 30, 1949, for Acousticapparatus, and Serial No. 99,650, file-:1 April 30, 1949, for Sounddistributing apparatus."

The inventor claims:

1. In an apparatus of the character described, in combination, a lowfrequency speaker, having a cone adapted to deliver sound waves from itsinner aswell as its outer surface, an enclosure for the speaker, onewall of the enclosure having an opening to pass the sound waves from thespeaker, means to support the speaker adjacent the opening, said supportincluding means defining a passage for sound waves from the front of thecone only through said opening, said support also providing a passagefor the sound waves from the back of the cone to the same opening, adirectional horn for receiving the sound waves from one of saidpassages, and means for rotating said born.

2. In an apparatus of the character described, in combination, a lowfrequency speaker, having a cone adapted to deliver sound waves from itsinner as well as its outer surface, enclosure 1" or the speaker, onewall of the enclosure having an opening to pass the sound waves from thes peameans to support the speaker adjacent the ope. ing, said supportincluding means defining a pas-- sage for sound waves from the front ofthe cone only through said opening, said s n ort also providing apassage for the sound waves from the back of the cone to the opening, adirectional horn for receiving the sound waves from said opening,

3. In apparatus for adding pitch tremolo to musical sounds devoid ofpitch tremolo, a cabinet,

stationary high and low frequency speakers in the cabinet, supportedrespectively adjacent the upper and lower ends thereof, a directionalhorn for each speaker rotatably supported in the cabinet, and means torotate the horns, there being openings in the cabinet to permit egressof sound.

4. In apparatus for adding a tremulant effect to musical sounds devoidof pitch tremolo, a stationary sound translating device, a rotatingdirectional horn having a sound channel opera-- tively associated withsaid device and extending transversely of the axis thereof, meansforming another sound channel operatively associated with said device,and means to control the passage of sound in said other channel.

'5. In apparatus for adding pitch tremolo to musical sounds devoid ofpitch tremolo, stationary sound translating mechanism, means forming arotating directional sound channel for said mechanism, means providinganother sound channel ior said mechanism, and means to alter the volumeof sound in one channel compared to that in the other channel.

6. In apparatus for adding pitch tremolo to musical sounds devoid ofpitch tremolo, sound translating mechanism, means forming a rotatingdirectional sound channel having a throat for cooperating with saidmechanism, and means to adjust the spacing between said throat and saidmechanism whereby the transfer of sound between said sound channel andthe translating mechanism may be varied.

'7. In apparatus of the character described, a sound translating device,means forming a pair of channels for simultaneous cooperation with saiddevice, means for imparting relative motion between one sound channeland the device for producing a tremulant efiect, and means foradjustably distributing the sound between the two channels.

8. In combination, means forming a common source of energy for producingsound waves, means providing separate sound channels cooperatingsimultaneously with said common source, means whereby one of saidchannels may be moved cyclically for producing a tremulant effect, andmeans for adjustably distributing the relative amounts of energy betweensaid channels.

9. In apparatus for adding pitch tremolo effects to musical sounds, apair of stationary sound translating devices having different frequencyranges, a common source of electrical impulses for both said devices, apair of means defining air columns, respectively associated with eachdevice, each air column having an opening for emitting sound, and meansfor rotating both of said air column defining means in such manner as tocause an orbital motion of said openings.

10. In apparatus for adding pitch tremolo effects to musical sounds, apair of stationary sound translating devices having difi'erent frequencyranges, a common source of electrical impulses for both said devices, apair of means defining air columns, respectively associated with eachdevice, each air column having an opening for emitting sound, andindependently controllable means for independently rotating each of saidair column defining means in such manner as to cause an orbital motionof said openings.

11. In a tone producing apparatus for an electrical musical instrument,the combination of a pair of loud speakers connected to receive theoutput of the instrument, one of said speakers being particularlydesigned to produce tones of a higher audible frequency range, while theother speaker is designed to produce predominantly the tones of thelower audible frequency range, a rotatable elbow-like deflectorpositioned to receive the acoustic output of said higher frequencyspeaker, and means to rotate said deflector at a speed in the order ofseven revolutions per second.

12. In a tone producing apparatus, the combination of pair oftranslators for converting electrical impulses into sound, one of saidtranslators being designed to produce predominantly tones of the higheraudible frequency range, the other translator being designed to producepredominantly the tones of the lower audible frequency range, a commonsource of electrical impulses connected to both of said translators,means forming a rotatable air column channel positioned to receive theacoustic output of said high frequency translator, said channel formingmeans having a sound emitting opening, and means to rotate said channelforming means to cause the sound emitting opening to describe a circularpath at a speed of the order of seven revolutions per second.

1.3. In a device of the character described, a stationar speaker, adirectional horn associated with the speaker, means forming an enclosurefor the speaker and the horn. a rotatable support for the horn, andmeans to revolve the horn, there being peripheral openings about theenclosure substantially aligned with the opening of the horn.

DONALD J. LESLIE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Published by Prentice-Hall, Inc., '70 FifthAvenue, New York, N. Y. (pages 22 to 26). i

